The Fields list shows fields for the table selected in the Selected Tables list.
Table Field: Shows the name of the field.
Preview: A preview of the data in that field.
Ent Id: Entity Id. You must select the radio button in one of the rows of this column. The Entity Id uniquely identifies each entity. By selecting a radio button you indicate which field of the table has the entity id. By using the Entity Id we're able to join data in different tables to form a single graph. For instance if we are to create relationships between this type of entity in another table, those tables must have a field where the values correspond to this entity id field.
Attrib: The Attribute column indicates that the field is an attribute of the entity type. Most fields that are relevant to the Entity Type / Entity Id become attributes.
Ignore: Select Ignore if we don't care about this field.
The Selected Tables list shows a list of tables associated with the Entity Type. When an entity type is first added, the Selected Tables list will only show the one table selected from the Choose A Table dialog.
An entity type can have one or more associated table as described in the Overview. A common case where more than one table would be associated with an entity type is if there is a table such as "People" which contains attributes of a person such as name, address, date of birth, and another table such as "Friendships" which contains relations between People. If the name of the person is used as the Id of the entity type, that name would be used 3 times, once in the "People" table and twice in the "Friendships" table.
The Apply button saves changes to the Entity Name, or the Field radio buttons. Changes must be applied (saved) before a new table can be added. After Apply is pressed, hitting Cancel at the bottom of the dialog will no longer cancel changes made before pressing the apply button.
The Add button is used to add another table using the Choose A Table dialog. You should do this if there are two or more tables containing attributes for the entity.
The Delete button removes the table from the Entity Type. To delete the only table associated with an entity type you need to delete the entity type instead.